The isdone.dll error is caused by your system being unable to utilize enough system resources to unpack the installation files present in a game. Lack of RAM, not enough HDD space or corrupted game files are the most common cause.

The core problem is that your system cannot hold enough data in memory. Each time you install a game, or any other large application, there are a large number of files (GB's in size) which have to be "unpacked". If you're seeing the isdone.dll/unarc.dll error, it means your computer does not have enough memory to unpack these files (or at least the memory to access them).

The solution is to first ensure that your system is running correctly (there are no issues). From here, you'll want to try several fixes to see if they are causing the problem; with a final solution of increasing the Windows virtual memory size if the error persists.

This tutorial explains exactly what to look for and how to manage the error.

Lack Of RAM

The isdone.dll error is indicative of low memory on your system.

All computer systems use something called RAM (Random Access Memory). This is kept in a volatile state when the system is powered-on, giving your OS a place to store data & access it as required / "randomly" (hence the name).

Everything from running the OS to holding applications in memory is handled through the RAM. It's the place where almost all operations of the system are stored.

Think of it like this - the CPU can only handle a certain number of instructions each second (this is measured by the speed/GHZ of the CPU). In order to manage these instructions properly, the computer requires a "queue" in which to store instructions, operations and responses. This queue is handled by the RAM - the larger the RAM capacity, the more of a queue can be stored & the more instructions can be handled.

This is why when you see computers, their CPU, RAM and HDD capacity is such an important factor. The problem you have is that because installing a game requires a large amount of RAM to be present, it is often the case that the RAM's queue has become too full, preventing your system from being able to handle the installation. This is the main cause of the infamous isdone.dll error.

To fix the error, you need to ensure that the RAM & system's available memory (which can use the HDD) are as high-capacity as possible. To do this, you need to remove any running operations from the OS (removes their instructions from the RAM queue) and also maximize the capacity of storage on your system.

This can be done with the following steps:

1. Close Programs

The first step is to close down other programs.

To do this, you should load Task Manager by pressing CTRL+ALT+DEL on your keyboard. This will bring up an application from which you need to select any program that appears, and press "End Process".

This is important, as if you have the likes of a web browser or other applications running along side your installation, the resource usage of the other apps will prevent your computer from being able to manage the game installer.

After loading it, you need to select "Processes" and remove any you can either recognize, or see on the Windows task bar. This will remove the majority of applications that are taking up extra resources.

Ultimately, the best thing to do is remove every process that isn't the installer. This way, you know the installer is getting the most resource allocation. If you don't know how to do this, it may be advisable to look up a tutorial on how to apply it.

2. Replace DLL's

The next step is to replace DLL files.

Whilst this will typically not work, it's a good way to ensure the system is working correctly.

To briefly explain, all x86/x64 operating systems have the capacity to load external libraries (pre-programmed applications) which are able to deliver specific functionality to the current application. In Windows, these files are known as Dynamic Link Libraries (DLLs), in Linux & OSX they are known as Shared Object (SO) files.

In the case of any DLL error on a system, it is often indicative of the DLL file being damaged, corrupted or incompatible with your version of Windows. Whilst the isdone.dll error is typically not the result of these problems, it will definitely help to replace the files, ensuring you have the latest & most stable versions on your PC.

Doing this is very simple -

You need to obtain isdone.dll and unarc.dll from a reliable source

Once you've obtained replacement versions of these files, copy them from your HDD

Browse to C:/Windows/System32

Right-click and select "Paste"

Restart your PC

The main benefit to doing this is to ensure that your computer is able to rely on the files necessary to install the game you need. In many cases, it can be the case that the various DLL files on Windows can be overwritten by incompatible / out of date versions that will lead your system to show weird errors like the one you've been seeing.

3. Test Memory

Next, you'll want to see if there is a hardware-level issue with your system's RAM.

As mentioned, the cause of isdone.dll errors is a lack of RAM, but what most people don't realize is that a faulty set of RAM can also cause similar errors.

It could be the case that your computer's RAM is damaged, preventing the system from accessing the archive data that it requires to install onto your hard drive.

It's quite a common issue for RAM to fail and cause intermittent problems for a system. Unlike other essential computer components, it can function at 50% or even lower capacity, and Windows will still operate (due to its "volatile" nature, the system expects the RAM to fluctuate in capacity).

To ensure this is not the case, there are a number of memory diagnostic tools you can use to test the physical integrity of your system's RAM.

Windows has an inbuilt tool called Windows Memory Diagnostic and there is a commercial tool called MemTest86 which does the same thing. These tools perform a test of the physical RAM by running certain voltages through it before Windows loads. The responses of the voltages gives Windows the opportunity to determine if the RAM is operating at full capacity or not.

To use them, you need to follow these steps (requires restart):

Press Windows Key+R on your keyboard (loads the "Run" dialogue)

Into this dialogue, type "mdsched.exe" & press OK

This will load up the "Windows Memory Diagnostic" interface

Click "Restart Now (Recommended)"

Wait for the system to restart

After restarting, the system should enter a "test" which will identify and determine whether any of the RAM on the system is damaged. You need to let the test run (will typically take around 5 minutes), and then see the results afterwards. If there are any issues, you need to look at either replacing or fixing any of the potential damage with the RAM itself.

4. RAM Removal

IF the memory test fails, it means that your system's RAM is physically defective.

This is not as bad as it sounds, but does mean you will need to replace at least one of the sticks in your system. Obviously, this means you'll have to access the inside of the system, which can be difficult. My most earnest recommendation is to seek professional help IF you are unable to do this (most people can).

If you have experience, or are confident enough to remove RAM on your own, you'll need to access the RAM ports of your computer (this varies from device to device), and remove a stick of the RAM inside. Obviously, a computer cannot run with zero sticks of RAM, so if this is the case you will need to either find replacement RAM (perhaps from a friend) or buy a new stick.

The best thing to do if you don't have replacement RAM lying around is to take it to a professional computer support company. This may cost, but at least you won't risk damaging your system (which can happen if you use the wrong RAM).

Removing faulty RAM won't fix isdone.dll, but will perhaps ensure that Windows is able to utilize its memory correctly. It is often the case that Windows will become "confused" if a RAM is intermittently faulty, as it is prevented from accessing sectors that should be present.

Removing a faulty stick solves this problem, but obviously leaves you without the necessary capacity to continue resolving the core error.

5. Virtual Memory

Finally, this trick solves 90% of isdone.dll errors.

The Windows Page File ("Virtual Memory") is an HDD file which the operating system uses as an "overflow" for RAM. It is also known as a "swap" file in other operating systems.

If the above steps did not fix the issue, you will need to increase the size of this file, allowing the system to utilize more hard drive space as a replacement for RAM. If your system really does not have enough RAM resource to complete the operation, this should resolve the problem.

Whilst this will solve the majority of isdone.dll/unarc.dll errors, it's not a permanent solution and should NOT be treated as such. If you wanted to resolve the issue permanently, you need to increase the RAM capacity of your system. Paging/Swap files can cause slowdown on your system as Windows has to access the HDD rather than the much faster RAM.

To do this, you need to follow these steps:

Windows 7

Click on "Start" > right-click "Computer" > select "Properties"

On the dialogue that shows, click "Advanced System Settings" (left hand menu)

Windows 10

Right-click on the "Start" button (bottom left of task bar)

Select "System"

Select "System Info" (right hand side)

Click "Advanced System Settings" (left hand menu)

From the "Advanced System Settings" dialogue, select "Settings" in the "Performance" tab.

In the new Window that shows, click on "Change" under "Virtual Memory".

Uncheck "Automatically manage paging file size for all drives" and then click "Custom Size", to which you should allocate around 5gb. This is obviously *not* recommended for normal operation, but since your system requires that level of data to install your game, you'll be best to set it at that level for now.

After doing this, click "OK" and then exit the system management window.

Turning back to the game installer, you should attempt to run it again. If it works, you should follow the above steps again to reset the page file to the automated size again. If it doesn't work, it means your system does not have the hardware capacity to perform the operation.

Conclusion

If you're still experiencing problems, you'll either need to replace your RAM or ensure you have set a large enough "Page File".

In 90% of cases, increasing the Windows paging file size should resolve the problem.